Norovirus

What are noroviruses?

Noroviruses are a group of related viruses that affect the intestinal tract
causing gastroenteritis illness. This group of viruses has been also referred
to as caliciviruses and Norwalk-like viruses. These viruses are an important
cause of gastrointestinal illness throughout the United States, including
Illinois.

What are the symptoms of noroviruses?

Many of the noroviruses cause similar symptoms that usually occur between 24
hours and 48 hours after exposure. They include nausea, vomiting, diarrhea,
abdominal pain, body aches, headache, tiredness and low-grade fever. Symptoms
typically last 24 hours to 60 hours and subside on their own. There are no
known long-term effects after recovery from this infection.

How common is norovirus infection?

The U.S. Centers for Disease Control and Prevention estimates that at least
half of all foodborne outbreaks of gastroenteritis can be attributed to
noroviruses. Some studies indicate that more than 60 percent of the U.S.
population is exposed to one or more of these viruses by the age of 50.
Noroviruses are highly contagious and can spread easily from person to person.

How do people come in contact with these viruses?

Humans are the only source for these viruses. These viruses do not multiply
outside the human body. The viruses are present in the feces of infected
persons and can be transmitted to others when hands are not thoroughly washed
after having a bowel movement. When an infected person who did not wash hands
after toileting handles food that is not later cooked, others who eat the food
can become infected. Heating foods to cooking temperatures kills these viruses.
People also can be infected by drinking water contaminated by sewage containing
one of these viruses or by consuming ice made from contaminated water. Unless
thoroughly cooked, shellfish (such as oysters) harvested from waters containing
sewage can transmit the viruses. These viruses also are transmitted readily
from person to person when hands are not washed after toileting. There is some
evidence that the viruses can be transmitted by aerosolized vomitus or contact
with objects contaminated with fecal material.

How are these infections diagnosed?

Standard hospital laboratories and commercial laboratories usually are not
equipped to detect noroviruses. The specialized laboratories that can detect
these viruses perform tests on stool specimens from an infected person to
detect the virus. In Illinois, only the Illinois Department of Public Health's
laboratories have the capability to confirm a diagnosis of one of these
viruses. This laboratory service is reserved for testing a small number of
people associated with recognized outbreaks and is not available for testing
individual cases of gastrointestinal illness.

If I have had a norovirus infection in the past, can I get it again?

Yes. It appears that immunity following norovirus infection varies from
person to person. It is possible some persons achieve immunity but more studies
are needed to better understand susceptibility to reinfection.

How can these infections be prevented?

Food handlers should practice careful handwashing after toileting and before
food preparation. Food handlers should not have bare hand contact with ice.
Persons involved in food preparation who have symptoms of gastroenteritis
should be restricted from work until they no longer have diarrhea. Water
supplies should be protected from the risk of contamination by sewage. Plumbing
in dwellings and business establishments should be constructed with no
cross-connections to prevent sewage from entering the drinking water supply.

All persons can decrease their chance of coming in contact with noroviruses
by following these preventive steps:

Frequently wash your hands, especially after toileting or changing diapers
and before eating or preparing food.

Thoroughly clean and disinfect contaminated surfaces immediately after an
episode of diarrhea or vomiting by using a bleach-based household cleaner. If
using liquid household bleach prepared daily, one part bleach to nine parts
water (1:10 dilution) is recommended.

Immediately remove and wash clothing or linens that may be contaminated
with feces or vomitus (use hot water and soap).

Flush or discard any vomitus and/or stool in the toilet and make sure that
the surrounding area is kept clean.

Persons who are infected with norovirus should refrain from food
preparation while they have symptoms and for three days after they recover from
their illness.

Outbreaks of norovirus in long-term care facilities are not uncommon and are
frequently transmitted from person to person (including residents, staff,
visitors and volunteers). Strict compliance with good hygiene practices is
important to prevent the spread of norovirus in this population.